In semiconductor devices, photodiodes, a type of diode that receives light and generates current, are widely used as the light-receiving element for an optical pickup device contained in a CD, DVD and other optical disk devices. The photodiode is made of a pn-junction semiconductor. When a reverse bias is applied to the pn junction, the depletion layer becomes wider, and a high electric field forms. Due to the light absorbed mainly by the depletion layer, electron-hole pairs are generated, and electrons attracted by the electric field move to the n-type semiconductor region, while the holes move to the p-type semiconductor region, and they are detected as current.
The aforementioned photodiodes include the following types: a PIN photodiode, which has an intrinsic layer, such as a p− layer or n− layer containing a low-concentration electroconductive impurity set between the p-layer and n-layer, and a depletion layer that can spread easily under a low voltage, and an avalanche photodiode that has a region where avalanche breakdown takes place. For example, the aforementioned photodiodes are disclosed in Japanese Kokai Patent Application No. 2001-320079.
It is well known that when said photodiode is assembled on an assembly substrate, the structure is sealed, e.g., with a clear molding resin. FIG. 5 is a cross-sectional view illustrating an example of a semiconductor device with said structure with clear molding resin applied for sealing after said photodiode is assembled on the assembly substrate.
For example, n-type semiconductor layer 101 is formed on the outer layer portion in the light-receiving region of p-type semiconductor substrate 100, and it is connected to a photodiode or the like. Then, pad electrode 102 is formed on the surface of semiconductor substrate 100 to form semiconductor chip T with a photodiode formed on it. By means of adhesive film 103, semiconductor chip T with said constitution is mounted on assembly substrate 104. Substrate electrode 105 is formed on assembly substrate 104, and, by means of wire bonding 106, pad electrode 102 of semiconductor chip T and substrate electrode 105 of assembly substrate 104 are connected.
Also, resin layer 107 made of a clear molding resin is formed to seal substrate electrode 105 and wire bonding 106 in the region connected to semiconductor chip T and wire bonding 106. Said resin layer 107 is made of a resin that is at least transparent to light received by the photodiode, and it can protect the photodiode and the wiring connecting portion without impeding the incidence of light.
The semiconductor device with photodiode assembled as aforementioned should have an area appropriate for connection with the wire bonding. Also, the resin layer of the clear molding resin is thick, such that it is difficult to reduce the overall size of the device. This is undesirable. Also, the manufacturing method has many steps of operation, and it is difficult to cut the manufacturing cost, and this is undesirable.